Characterisation of wet and dry spells and associated atmospheric dynamics at the Pra River catchment of Ghana, West Africa

Abstract

Study region: The Pra river catchment in Ghana, West Africa. Study focus: Knowledge of the spatio-temporal distribution of wet and dry spells are crucial for rain-fed agriculture at the Pra River catchment. This study characterised spells and their associated atmospheric dynamics at the Pra river catchment. Specifically, the variability of historical and future wet and dry spells and atmospheric dynamics on the rainfall and spell patterns at the catchment were studied. New hydrological insights: Short duration spells have a higher occurrence at the catchment as compared to long duration spells. Seasonally, short duration dry spells are most common in December–February, whereas wet spells are expected in March–May. Future scenarios show an increase in both wet and dry spells. Composites of the atmospheric dynamics for 2–3 day dry spells show moisture convergence over the entire catchment, with lower total column water levels. However, there is a dipole of moisture convergence and divergence for wet spell composites, with higher than normal total column water. An anticyclonic circulation, inducing a ridge at 500 hPa, coupled with low-level southerlies at 850 hPa act to support wet spell occurrences in JJA. The findings contribute to sub-seasonal and seasonal forecasting, and hence will improve agricultural practices in the catchment in support of food security.

Keywords

• Wet and dry spells
• Atmospheric dynamics
• Representative concentration pathways (RCP)